What are the load-bearing tropes for Gygaxian D&D?
- The adventuring environment – dungeon, wilderness – must be unknown. The PCs should therefore come from somewhere else.
- The adventuring environment must contain things the players want – treasure, magic items.
- The adventuring environment must contain things the players want to avoid – wandering monsters, traps.
- The adventuring environment must be large so there are many meaningful decisions to be made about where to go.
- The adventuring environment should be lawless so no one can force the PCs to do anything.
- If there are a lot of different 'grades' of monster and treasure then it makes the players' decisions more meaningful.
- The existence of magic makes the DM's job much easier, in much the same way it makes a pulp fantasy writer's job easier.
- The PCs should be detached from society – more like Conan than Frodo – so they are free to go anywhere they want.
Therefore I'd say the load-bearing tropes are:
- Civilisation vs wilderness.
- Lots of magic.
- Lots of monsters and other hazards.
- Big dungeons or wildernesses.
- PCs are rootless wanderers.
(2) and (3), to the extent that D&D embraces them, don't look like most of its sources in fiction, except to some extent Vance's Dying Earth and to a greater extent, the kitchen sink universes of Marvel and DC comics.
I don't think Evil monsters are essential. Good and evil seem entirely unnecessary to this power up finding, peril avoiding game. Monsters are evil from the PCs' perspective insofar as they prevent them getting what they want, but they don't have to be cosmically Evil.